Particular combustion systems for gas turbine engines utilize combustors having bundled tube type fuel nozzles for premixing a gaseous fuel with a compressed air upstream from a combustion zone. A bundled tube fuel nozzle generally includes multiple tubes that extend through a fuel plenum which is at least partially defined between a forward plate, an intermediate plate and an outer sleeve. Compressed air flows into an inlet portion of each tube. Fuel from the fuel plenum is injected into each tube where it premixes with the compressed before it is routed into the combustion zone.
A portion of each tube may be rigidly connected to the intermediate plate while a downstream end or tip portion is unsupported, thereby creating a cantilevered tube. The downstream end or tip portion of each tube extends through a corresponding tube opening defined in an aft plate which is axially spaced from the intermediate plate and positioned proximate to the combustion chamber. A circumferentially continuous radial gap is defined between an outer surface of each tube at its tip portion and the corresponding tube opening in the aft plate to allow for a cooling fluid such as compressed air to flow around the tube towards the combustion chamber, thereby cooling the tip portion. During operation, the tip portion of each tube may vibrate causing potentially resulting in undesirable wear between the individual tubes and the aft plate.